In the semiconductor industry, integrated circuits are made using photolithographic processes that rely upon a series of different photomasks to define different structural features of the circuit. The pattern on each photomask is designed to conform to dimensional rules that ensure that the patterns transfer properly and the integrated circuit functions properly. Once the layout is created as a pattern on the photomask, the photolithographic process utilizes an exposure tool to project the mask pattern onto a layer of photoresist carried on the semiconductor wafer.
A satisfactory product yield is contingent upon having essentially defectless masks and reticles. Photomask deployment may result in relatively high mean time to detect (MTTD) for the appearance of new mask-related defects or the occurrence of mask degeneration. Poor handling of a photomask may dislodge otherwise innocuous particulates and cause relocation to positions on the photomask that ultimately cause defects in the wafers fabricated using the photomask. In any event, degradation of the photomask may cause yield loss in the integrated circuits fabricated using the photomask.
As an important step associated with the photolithography process, wafer fabricators periodically inspect every photomask after a fixed number of wafer passes to determine the condition of the photomask. Unfortunately, high resolution mask inspection tools, such as CCD imaging systems, are typically only found in mask fabrication shops. Wafer fabricators may have only a limited ability to monitor the photomask condition because of the absence of a high resolution mask inspection tool. In any event, photomask inspection does not provide real-time monitoring of contamination on the photomask, the environment of the photomask, or a physical attribute of the photomask.
Accordingly, there is a need for an improved apparatus capable of providing contamination, environmental, or physical monitoring of a photomask.